Ammonia is an important chemical material and energy material. Nitrogen atoms are important constituent of bio-molecules, and thus are essential component of medicaments and fertilizers. Moreover, nitrogen atoms are widely used in non-biological fields such as dyes, explosives, and resins. The synthesis of all these materials requires ammonia as the raw materials. Besides, ammonia is also an important energy material. Hydrogen is produced by the decomposition of ammonia, and therefore, ammonia is widely used as a hydrogen storage material.
Ammonia synthesis with nitrogen in air is considered to be the greatest scientific advance in 20th century, and more than 1% of the total energy in the world is used for ammonia synthesis per year. At present, Haber-Bosch process is mainly used for artificial ammonia synthesis, which is a thermal catalytic technology. During the Haber-Bosch process, nitrogen and hydrogen serve as reaction gas, and reaction occurs under a high temperature and high pressure reaction condition with a Fe-based or Ru-based catalyst. However, during thermal catalysis procedure (with temperature ranging from 300° C. to 550° C., and pressure ranging from 15 megapascal (MPa) to 25 MPa), a large amount of fossil fuel needs to be consumed, and the burning of fossil fuel would result in greenhouse gas (carbon dioxide) emission. Facing the energy problem and environmental problem which draw increasingly attention throughout the world, energy conservation and emission reduction are always huge challenges in ammonia synthesis industry.
Solar energy is a renewable energy which is clean and cheap, and is the ultimate source of most energy in the world. There is a great application potential to utilize sunshine directly. Solar thermal effect is widely used in solar thermal power generation, solar water heater, and other industries in China. However, there is still a huge challenge to use sunshine for driving chemical reaction. According to the solar thermal catalytic technology which is developed in recent years, the optical wave in whole spectrum range of sunshine can be utilized effectively. That is, semiconductor can be excited by optical wave of high frequency wave band to generate photo carriers and realize photo-catalytic reaction, and at the same time, thermal reaction can be promoted by thermal energy generated during photo generated carriers recombination and thermal energy from optical wave of infrared wave band in the sunshine. In this manner, the solar energy utilization rate and the catalytic reaction efficiency can both be improved effectively. However, ammonia synthesis under normal pressure still remains challenging. Since in nitrogen, N—N triple bond is rather stable (the bond energy thereof is as high as 946 KJ/mol), and nitrogen cannot be activated by catalysts reported by related documents. Chinese patent (CN104016825A) discloses a Fe-containing or Ru-containing catalyst, which is used for producing organic fuel through carbon dioxide conversion, but cannot be used during ammonia synthesis reaction with nitrogen and hydrogen (the specific result thereof is shown in Table. 1).
Therefore, a technology through which solar energy can be absorbed and utilized effectively for catalyzing ammonia synthesis with nitrogen and hydrogen under solar energy is in demand. The technology has a great significance for both environment and energy, and the production cost of ammonia can be reduced. In a word, the technology has a bright commercial prospect.